The present invention relates to a control system for an internal combustion engine that performs catalyst temperature rise acceleration control for accelerating a rise in temperature of a catalyst for exhaust gas purification, and more particularly to such a control system having a function of diagnosing a failure to properly perform the catalyst temperature rise acceleration control.
A catalyst for exhaust gas purification is provided in the exhaust system of an internal combustion engine. This catalyst is inactive at low temperatures. Consequently, the catalyst does not purify the exhaust gas at low temperatures. Therefore, it is desirable to rapidly raise the temperature of the catalyst, immediately after starting the engine, to activate the catalyst.
Known in the art is a technique for accelerating the rise in temperature of the catalyst. This technique increases the intake air amount immediately after starting of the engine as compared with the air intake amount at normal idling of the engine. The technique also controls the ignition timing in a retarding direction so that the rotational speed of the engine coincides with a target rotational speed (Japanese Patent Laid-open No. 10-299631). According to this technique, the fuel supply amount increases with the increase in the intake air amount. Thus, the combustion heat increases immediately after starting of the engine as compared with that at normal idling. The immediate combustion heat increase enables the acceleration of the temperature rise in the catalyst.
However, the above-mentioned conventional technique makes no provision for detecting a failure to execute instructions from the control unit. For example, a failure to increase the intake air amount and/or a failure to change the ignition timing to the retard side are not detected. Accordingly, in the event that such a failure has occurred, the driver may not notice the failure, causing a deterioration in exhaust emission characteristics immediately after starting of the engine.
It is accordingly an object of the present invention to provide a control system for an internal combustion engine that can diagnose a failure to execute the catalyst temperature rise acceleration control, including the increase in the intake air amount and the retard control of the ignition timing in combination, and thereby minimize a deterioration in exhaust emission characteristics.
In accordance with an aspect of the present invention, there is provided a control system for an internal combustion engine having an exhaust system provided with a catalyst, comprising intake air amount control means for controlling an intake air amount to the engine, ignition timing control means for controlling an ignition timing of the engine, catalyst temperature raising means for increasing the intake air amount after starting of the engine and for retarding the ignition timing according to a rotational speed of the engine, and failure diagnosing means for diagnosing a failure of the catalyst temperature raising means according to at least one of the rotational speed of the engine and a retard amount of the ignition timing during the operation of the catalyst temperature raising means.
With this configuration, the failure of the catalyst temperature raising means is diagnosed according to at least one of the rotational speed of the engine and a retard amount of the ignition timing during the operation of the catalyst temperature raising means. Accordingly, any failure in the catalyst temperature raising means can be diagnosed early to thereby minimize a deterioration in exhaust characteristics.
Preferably, the failure diagnosing means determines that the catalyst temperature raising means has failed when the rotational speed of the engine after the elapse of a predetermined time period from the time of starting the operation of the catalyst temperature raising means is less than or equal to a predetermined rotational speed.
Preferably, the failure diagnosing means determines that the catalyst temperature raising means has failed when the retard amount of the ignition timing after the elapse of a predetermined time period from the time of starting the operation of the catalyst temperature raising means is less than or equal to a predetermined retard amount.
Preferably, the failure diagnosing means diagnoses the failure of the catalyst temperature raising means according to a crank angle position at which the rotational speed of the engine during the operation of the catalyst temperature raising means becomes maximum.
With this configuration, the failure of the catalyst temperature raising means is diagnosed according to the crank angle position at which the engine rotational speed during the operation of the catalyst temperature raising means becomes maximum. Accordingly, the failure can be determined from the result of determination whether or not the retard control of the ignition timing is accurately performed from a crank angle position at which ignition actually occurs. Accordingly, it is also possible to determine such a failure when an actual ignition timing is different from a generation timing of an ignition timing control signal.
Preferably, the failure diagnosing means diagnoses the failure of the catalyst temperature raising means according to an amount of change in the ignition timing during the operation of the catalyst temperature raising means.
With this configuration, the failure of the catalyst temperature raising means is diagnosed according to an amount of change in the ignition timing during the operation of the catalyst temperature raising means. Accordingly, the determination can be accurately performed even in the case that the ignition timing is generally shifted to the advance side or the retard side.
Preferably, the control system further includes intake air temperature detecting means for detecting an intake air temperature to the engine and coolant temperature detecting means for detecting a coolant temperature of the engine, wherein the failure diagnosis by the failure diagnosing means is inhibited when the difference between the detected coolant temperature and the detected intake air temperature is greater than or equal to a predetermined temperature.
Preferably, the control system further includes load detecting means for detecting a load on the engine, wherein the failure diagnosis by the failure diagnosing means is inhibited when the detected load is less than a predetermined value.
Preferably, the catalyst temperature raising means operates when the rotational speed of the engine is greater than or equal to a predetermined lower-limit rotational speed and the engine is in an idling condition.
Preferably, the control system further includes coolant temperature detecting means for detecting a coolant temperature of the engine, wherein an operating time period of the catalyst temperature raising means is set according to the detected coolant temperature at starting of the engine.
Preferably, the catalyst temperature raising means sets the retard amount of the ignition timing so that the rotational speed of the engine coincides with a target rotational speed.
In accordance with another aspect of the present invention, there is provided a control system for an internal combustion engine having an exhaust system provided with a catalyst, comprising intake air amount control means for controlling an intake air amount to the engine, ignition timing control means for controlling an ignition timing of the engine, catalyst temperature raising means for increasing the intake air amount after starting of the engine and for retarding the ignition timing according to a rotational speed of the engine, and failure diagnosing means for diagnosing a failure of the catalyst temperature raising means according to at least one of the ignition timing and the rotational speed of the engine when decreasing the intake air amount during the operation of the catalyst temperature raising means.
With this configuration, the failure of the catalyst temperature raising means is diagnosed according to at least one of the ignition timing and the engine rotational speed when decreasing the intake air amount during the operation of the catalyst temperature raising means. Accordingly, any failure in the catalyst temperature raising means can be diagnosed early to thereby minimize a deterioration in exhaust characteristics.
Preferably, the failure diagnosing means determines that the catalyst temperature raising means has failed when the absolute value of the difference between the rotational speed of the engine and a predetermined rotational speed is greater than a predetermined value.
Preferably, the failure diagnosing means determines that the catalyst temperature raising means has failed when an amount of change in the ignition timing is less than a predetermined amount.
In accordance with a further aspect of the present invention, there is provided a control system for an internal combustion engine having an exhaust system provided with a catalyst, comprising intake air amount control means for controlling an intake air amount to the engine, ignition timing control means for controlling an ignition timing of the engine, catalyst temperature raising means for increasing the intake air amount after starting of the engine and for retarding the ignition timing according to a rotational speed of the engine, catalyst temperature detecting means for detecting a temperature of the catalyst, catalyst temperature estimating means for estimating a temperature of the catalyst, and failure diagnosing means for diagnosing a failure of the catalyst temperature raising means according to the temperature detected by the catalyst temperature detecting means and the temperature estimated by the catalyst temperature estimating means.
With this configuration, the failure of the catalyst temperature raising means is diagnosed according to the catalyst temperature detected by the catalyst temperature detecting means and the catalyst temperature estimated by the catalyst temperature estimating means. Accordingly, any failure in the catalyst temperature raising means can be diagnosed early to thereby minimize a deterioration in exhaust characteristics.
Preferably, the catalyst temperature estimating means estimates the temperature of the catalyst according to an accumulated value of the intake air amount after starting of the engine.
Preferably, the catalyst temperature estimating means estimates the temperature of the catalyst according to an elapsed time period after starting of the engine.
Preferably, the failure diagnosing means determines that the catalyst temperature raising means has failed when the absolute value of the difference between the temperature detected by the catalyst temperature detecting means and the temperature estimated by the catalyst temperature estimating means is greater than a predetermined value.